Additive for copper plating bath



Feb. 13, 1962 s ow ETAL 3,021,266

LATING BATH Vi X1 MM )W M WM WWW mu HM Unite States The present invention is directed to Electro-plating and more particularly the plating of bright copper for the purpose of obviating excellent leveling of the de posit.

Previously, in ordinary cyanide copper plating baths all of the deposits resulting from such baths have had a negative leveling, namely, that the surface roughness after the plating operation was greatly magnified. Such negative leveling is described in the literature, and reference is here made to an article entitled, A Study of Leveling in Cyanide Copper Baths by Ostrow & Nobel, appearing in Proceedings of the American Electro- Chemical Society, vol. 41, p. 125. With cyanide copper baths it has only been possible to secure leveling by the use of an addition agent and also with application of periodic reverse current. The use of such periodic reverse current is undesirable because it tends to remove the copper deposit from the basis metal in order to produce the leveling or smoothing effect.

Another disadvantage of the use of periodic reverse current is that it requires special electrical equipment adding to the cost of operation and utilizing equipment which requires attention.

The present invention is intended to overcome the difficulties and disadvantages inherent in prior methods, it being among the objects of the present invention to deposit from cyanide copper baths, platings which are lustrous and bright and exhibit leveling, and Without the necessity of the use of periodic reverse currents.

It is also among the objects of the present invention to provide a cyanide copper plating bath wherein the deposits are bright and level over a wide range of current densities.

It is further among the objects of the present invention to provide a bath which enables a substantial reduction of the amount of mechanical polishing necessary on metal parts prior to or after plating by depositing the copper from a bath having leveling properties.

It is still further among the objects of the present invention to provide a bath of the character described which will not only provide leveling characteristics, but as the result of which, the deposits are highly adherent and ductile.

In practicing the present invention it has been discovered that leveling may be obtained by the use of a conventional cyanide copper bath by incorporating therein soluble compounds of arsenic and of lead within a predetermined and definite range of constituents. The concentration of these compounds is of primary importance and the ratio of arsenic to lead is also important in order to obtain the maximum results.

While the presence of arsenic and lead in the plating bath gives satisfactory leveling, much better results are obtainable if, in addition, there is present certain ethylene oxide derivatives which are surface active agents. With such additions the baths become particularly advantageous in commercial plating operations. Such derivatives have the following formula:

wherein R is an alkyl radical having 6 to 20 carbon atoms, R is an acid group designated by A-COOH in which A is an alkyl radical having 1 to 4 carbon atoms and n is 10 to 100. These compounds are effective even in the low current density areas. A number of com- *ten' pounds of this type is set forth in copending application Serial No. 636,862 filed January 29, 1957 and entitled, Improved Copper Plating Composition.

Excellent leveling effects are obtained even with very small amounts of the addition agents, as low as .00l'

which are quaternary nitrogen compounds. R" isan alkyl radical having 1 to 5 carbon atoms, and X is a negative radical, such as chlorine, bromine, iodine or sulfate; other negative radicals may be used, both inorganic andorganic, provided they are stable in the bath under the conditions of the operations. These quaternary compounds may also be used in conjunction with the above identified polyethylene oxide-fatty acid compounds.

It is common practice in the art to test the leveling characteristics of a plating bath to plate on a surface which has been preroughened to the extent of R.M.S. values of 2 040 micro inches, then depositing metal on said surface to a thickness of .5 to 1.0 mils and measuring the reduction of surface roughness. The results obtained by the present invention have been evaluated in accordance with this test. By the use of a combination of soluble arsenic compounds with soluble lead c'om pounds as addition agents in copper plating baths, it has been found that by starting with a basis metal having an R.M.S. of 34 micro inches and depositing 1 mil of copper, the R.M.S. is reduced to 10-15 micro inches and even lower.

The range of concentrations of arsenic and lead in the bath may vary within quite narrow limits; outside of these limits very little if any beneficial results are ob-' tainable. The arsenic present in the bath is within the limits of .01 to 1.50 grams per liter and the preferred range is .01 to .70 gram per'liter. The concentration of lead is from .02 to .30 gram per liter, with the preferred concentration of .02 to .15 gram per liter.

While various ratios of arsenic to lead may be used, the optimum ratio of arsenic to lead is 47 to 1. The maximum concentration of lead is about .30 gram per liter, but a lower concentration is highly desirable since the deposits of copper are more ductile. In conjunction with the arsenic less concentrations of lead are required to obtain the same degree of leveling. The arsenic in itself increases ductility of the deposit. When the bath contains compounds of ethylene oxide described herein,

still lesser concentrations of lead are required for the leveling and ductility.

Although leveling results in cyanide copper baths of a wide range of concentrations, the lower concentrations are preferred since they are simpler to control and they produce brightness and level over a wide range of cur- The concentrations of the metallic addirent densities. tion agents are, therefore, linked with the concentrations of copper cyanide.

The following are a number of specific examples showing the operation of the invention, they being typical of many baths coming within the scope of the invention.

Example 1 An aqueous copper cyanide plating bath having the Patented' Feb. 13,1962,

3 following "compos'ition'is'used, the amounts being in grams per liter:

CuCn 30.0

Total NaCN' 48.0 Free NaCN V 15.0 KOH 45.0 Pb (as soluble tartrate) .045 As (as Na Aso l .210 Ethyl quaternary of laurylamine polyethylene glycol 660 .040

The bath was operated at about 150 F. with mild agitation at '25 amperes per sq. ft. for a sufficient time to deposit 1 mil of copper.

In the accompanying drawing, FIG. 1' is an R.M.S..trace showing the surface before plating and having a value of 31 micro inches. After the platingthe surface had an R.M.S. value of 8 micro inches as shown in FIG. 2. In addition to the leveling action,.the frequency of the surface roughness has been almost eliminated.

bath was operatedat 140;" F. with mildagitation. A

bright leveled depositwas 'obtained on a Hull Cell panel in the range of 4-90 amperesper sq. ft:

The following bath was; used, the. constituents being present in the designated amounts in gramsper liter:

CuCN 60.0 Total NaCN; 81.0 Free NaCN 15.0 KOH 45.0 Pb:'(as acetate); .12 A's;(as .NH AsOg) .70 Methyl: quaternary of laurylamine polyethylene glycol 660 .20

The plating was conducted at 155 F. The deposit was lustrous overthe range of 10-80 ampcres per sq. ft. in a Hull Cell. It exhibited excellent leveling over a range of ,10-50 amperes per sq. ft.

Example-4 The bath was an all-potassium bath of the following composition in grams per liter:

CuCN.. V 45.0 TotalwKcN- 81.0 Free KCN; 18.0 KQH. 45.0 Pb.-(as citrate) .12 (as K2AS03) .56 Butyl quaternary, of. cetylaminepolyethylene glycol 660 .16

The temperature-of 'plating-was140 F. with mild agitation.; The deposit was lustrous and leveled over the Hull Cell range of-10-80 amperes per sq. ft.

Example The aqueous bath had the following composition in grams perrliter:

CuCN 30.0 Total KCN 60.0 Free KCN 18.0 KOH -a 45.0

Pb (as plumbate) As (as K arsenate) Methyl quaternary of laurylamine polyethylene glycol 600 .04

The temperature of plating was 145 F. with gentle agitation. The bright plating range on a 3-arnpere Hull Cell panel was from 5 to amperes per sq. ft. and leveling was obtained Over the above stated range.

Example 6 A bath of the following compositions in grams per liter was used in the plating operation:

CuCN 60.0 Total KCN 106.5 Free KCN 22.5

KOH 60.0 Pb (as plumbate) .18 As (as arsenate) .84

Methyl quaternary of laurylamine polyethylene glycol 600 A temperature of F. was maintained and the bath was gently agitated. The bright range on at Hull Cell panel was from 20-90 amperes per sq. ft. with satisfactory leveling. In Examples 5 and 6 the potassium formulations required larger amounts of the leveling agents than in the sodium formulations in order to obtain equivalent leveling effects.

Example 7 The following bath, expressed in grams per liter, in aqueous solution, was used:

CuCN 30.0 Free NaCN 15.0 KOH 75.0 P-b (as tartrate) .05 As (as Na AsO .16 Sodium acetate of laurylamine polyethylene gly-' col 660 .08

The temperature of plating was. F. No agitationwas applied. Both brightness and leveling on the plated surface were excellent over a Wide range of amperage.

Example. 8

The bath had the following composition expressed in grams per liter:

CuCN 37.5 Free NaCN 19.0 KOH 30.0 Rochelle salts 45.0 Pb (as saccharate) .10 As (as K AsO .50 Na-acetate of lauryl-amine polyethylene glycol 660 .10 Methyl quaternary of polyethyleneglycol 440 .05

At temperature ofplating of F., the leveling was satisfactory over a wide range in the .Hull Cell operation.

Example 9 The use of thallium as a replacement forat least part. of the lead is indicated in the following bath, the proper-- tions being in grams per liter:

CuCN 30.0

NaCN 47.0 KOH 45.0 As (as K AsO 0.2 Tl(as 11 50 0.008.

The bath was operated at 150 F. with mild agitation.

A Hull Cell panel plated at 2 amperes for 10 minutes:

showed a'biight range from'10 to 80 amperes per sq. ft. with leveling of the basis metal.

Example 10 Bismuth may be used with the arsenic and may replace lead in whole or in part. Such a bath has the following composition in grams per liter:

Bi (as NaBiO 0.008

The temperature of the bath was 155 F. with mild agitation. Leveling of the surface of the basis metal resulted.

In the commercial application of the present invention, it is preferred that the bath have a low copper cyanide content, within the range of 3 to 6 ounces per gallon. It is possible to obtain leveling in baths having the higher concentrations of copper cyanide, say 8 to 12 ounces per gallon, but-the plating range is substantially narrower.

What is claimed is:

1. An alkaline cyanide copper plating bath consisting of copper cyanide, alkali cyanide, alkali hydroxide, lead in the form of a soluble compound thereof, arsenic in the form of a soluble compound thereof, and a quaternary nitrogen compound, said arsenic and said lead being present in the ratio of 4-7 to 1, the amount of arsenic being about .01 to 1.5 g./l. and the amount of lead being about .02 to .30 g./1., said nitrogen compound having the formula R;N R" 2H; 0 .11 X H wherein R" is an alkyl radical having 1 to carbon atoms,

R is an alkyl radical having 6 to 20 carbon atoms, :1 is from 10 to 100 and X is a negative radical, said nitrogen compound being present in said bath in amounts of from .001 to 1.0 g./l.

2. A bath according to claim 1 wherein said lead is present as a compound taken from the class consisting of tartrate, plumhate, acetate, and citrate.

3. A bath according to claim 1 wherein said arsenic is present as a compound taken from the class consisting of arsenate and arsenite.

4. A bath according to claim 1 wherein said nitrogen compound is taken from the class consisting of ethyl quaternary of lauryl amine polyethylene glycol, propyl quaternary of lauryl amine polyethylene glycol, methyl quaternary of lauryl amine polyethylene glycol, and butyl quaternary of cetyl amine polyethylene glycol.

References Cited in the file of this patent UNITED STATES PATENTS 1,120,795 Daft Dec. 15, 1914 2,198,365 Cinamon et al Apr. 23, 1940 2,216,605 Sklarew et a1 Oct. 1, 1940 2,677,654 Chester et a1. May 4, 1954 2,689,216 Nevers et a1 Sept. 14, 1954 2,732,336 Ostrow Jan. 24, 1956 2,828,252 Fischer Mar. 5, 1958 2,841,542 Manquen July 1, 1958 2,848,394 *Foulke et al Aug. 19, 1958 2,859,159 Wernlund Nov. 4, 1958 OTHER REFERENCES Coats, Transactions Electromechanical Society, volume (1941), pages 445-57. 

1. AN ALKALINE CYANIDE COPPER PLATING BATH CONSISTING OF COPPER CYANIDE, ALKALI CYANIDE, ALKALI HYDROXIDE, LEAD IN THE FORM OF A SOLUBLE COMPOUND THEREOF, ARSENIC IN THE FORM OF A SOLUBLE COMPOUND THEREOF, AND A QUATERNARY NITROGEN COMPOUND, SAID ARSENIC AND SAID LEAD BEING PRESENT IN THE RATIO OF 4-7 TO 1, THE AMOUNT OF ARSENIC BEING ABOUT .01 TO 1.5G./. AND THE AMOUNT OF LEAD BEING ABOUT .02 TO .30 G./I., SAID NITROGEN COMPOUND HAVING THE FORMULA 